Under the circumstances of a recent rise in environmental problems, attention has been paid to hydroelectric power generation, wind power generation, and photovoltaic power generation as clean energy. Among these, photovoltaic power generation has seen a remarkable improvement in performance such as the power generation efficiency of solar cell modules, and an ongoing decrease in price, and national and local governments have worked on projects to promote the introduction of residential photovoltaic power generation systems. Thus, in recent years, the spread of photovoltaic power generation systems has advanced considerably.
By photovoltaic power generation, solar light energy is converted directly to electric energy using a semiconductor (solar cell element), such as a silicon cell. The performance of the solar cell element utilized there is deteriorated by contacting the outside air. Consequently, the solar cell element is sandwiched by an encapsulant or a protective film for providing buffering and prevention of contamination with a foreign substance or penetration of moisture. In order to efficiently apply sunlight to the solar cell element, the transparency of the encapsulant and protective film is required.
In consideration of these demands, with the intentions of improving the transparency of the sheet for solar cell encapsulant, the adhesion of the sheet for solar cell encapsulant to various members composing a solar cell module, and the appearance of the sheet, a protective sheet for solar cell module included an ethylene-vinyl acetate copolymer containing 20% to 40% by mass of vinyl acetate as the main polymer, a copolymer prepared from ethylene, vinyl acetate, and glycidyl (meth)acrylate as the secondary polymer, and an organic peroxide is disclosed (see, for example, Patent Document 1).
In addition, with the intention of improving heat resistance and durability of a sheet for solar cell encapsulant during long-term use in a natural environment, for example, a protective sheet for solar cell module, the protective sheet being molded from a composition included a copolymer containing an unsaturated carboxylate ester in place of a commonly used ethylene-vinyl acetate copolymer, is disclosed (see, for example, Patent Document 2).    Patent document 1: Japanese Patent Application Laid-Open (JP-A) No. 4-325531    Patent document 2: JP-A No. 4-311732